The neem tree, a tropical evergreen, has been used for centuries as a source of pesticides to which insects have not developed a resistance. Various neem seed extracts, particularly the ones containing the tetranortriterpenoid azadirachtin, are known to influence the feeding behavior, metamorphosis (insect growth regulating effect), fecundity, and fitness of numerous insect and fungal species belonging to various orders.
Neem seeds also contain various oily substances, at least one of which has been used for its medicinal and therapeutic properties for centuries. However, oils have been produced from neem seeds by a number of methods. This has lead to a great variability in the properties of neem oils. Very little chemical characterization has therefore been possible. Many of the publications referring to oils isolated from need seeds give no information as to its preparation, which is the key determinant of its composition.
There are two principle methods of obtaining extracts from neem seeds: expulsion, where the extract is pressed from the seeds, and extraction, where the extract is removed from the seeds by solubilization in a solvent. Inherently, materials made by these methods have very different properties. Extracts expelled from the seed will also contain water expelled from the seed by the same process. This aqueous material will carry along with it liminoids, such as azadirachtin, which themselves have pesticidal activity.
There are various methods known in the prior art to extract azadirachtin from neem seeds, including the use of solvents such as methanol, ethanol, water, methylene chloride, chloroform, hexane, methylethylketone, butanol, petroleum benzene, ether, acetone, methyl tertbutyl ether, diethylcarbonate, etc. In general, there have been two methods use to solvent extract materials from neem seeds. In one method, the neem seeds were ground and hydrophobic fatty acids and oils were removed by extraction of the seeds with a nonpolar solvent. The ground seeds are then extracted with a hydrophilic polar solvent to remove the hydrophilic, azadirachtin-containing neem fractions from the neem seeds. In a second prior art method, the neem seeds were first extracted with a polar solvent to remove the hydrophilic azadirachtin-containing fraction from the seeds. The hydrophilic residue was then extracted with a nonpolar solvent to remove residual hydrophobic fatty acid and oils.
Disadvantages often associated with prior art method heretofore used to extract azadirachtin from neem seeds include (1) the need to dry the seeds in a very temperature sensitive state; (2) cross-contamination of polar and nonpolar solvent streams; (3) water accumulation in the polar solvent streams; (4) co-extraction of very polar components, such as carbohydrates, which complicates downstream processing of the extract; (5) low azadirachtin concentrations or yields in the extract product; and (6) low oil recovery yields.